This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Though EMAN has been used successfully for icosahedral and asymmetric reconstruction of virus particles, the EMAN method of particle orientation refinement is a very CPU intensive process for large virus particles. One million CPU hours were consumed to determine the 4.5 [unreadable] map of the epsilon15 phage (Jiang et al., 2008) using the NSF supported TeraGrid computing facility . A similar structure determination using the clusters available at the NCMI combined with outside supercomputer allocations has taken over 12 months to refine a single structure of P22 phage from ~23,000 particle images. We, therefore, look for alternative methods for such large objects, with the same accuracy but a higher CPU efficiency.